Antifreeze and deicing fluids have been used for a number of years most notably in automotive engine systems and in deicing of aircraft. An antifreeze is a substance that is added to a liquid, usually water, to lower its freezing point. The largest single use of antifreeze is to protect liquid cooled internal combustion engines against freezing and consequent damage to the engine water jacket and the radiator. Various chemicals have been used in the past as antifreezes such as methanol, denatured ethanol, glycerol, calcium chloride, salt brines, and various glycols.
An acceptable antifreeze must satisfy many requirements. The most essential of these are the ability to lower the freezing point of water to the lowest winter operating temperatures likely to be encountered, satisfactory chemical stability and service, minimal effect on materials in contact with the antifreeze, and usefulness for at least one winter season. Although ethylene glycol is the most popular antifreeze today, several other substances are acceptable for special application.
Deicing chemical fluids are used chiefly for removing ice and frost from parked aircraft and from windows. The heated deicing chemical breaks the surface bonding of the ice which then can be readily removed by mechanical means, often by the force of the sprayed chemicals. Antiicing fluids are also used at airports after deicing has been completed to prevent subsequent ice formation on the cleaned surfaces. Antiicing is most often performed using a two-step procedure in which the aircraft is first deiced using a hot, high pressure fluid, and then antiiced using a cold fluid. Antiicing fluids serve to protect the cleaned surfaces from further accumulations of frozen deposits for a finite period of time.
Because of the time limited protection that deicing fluids provide, and because of the rapidly increasing air traffic and subsequent longer taxi times, thickened, non-Newtonian antiicing fluids are being used. These antiicing fluids contain glycols for freeze point depression, with added water, corrosion inhibitors, wetting agents, and stabilizers. These antiicing fluids also contain a polymeric thickening agent that gives the fluid its antiicing properties and which increases the fluid's viscosity, allowing the fluid to adhere to the aircraft surfaces.
In recent years, cable lines have been installed across the country to provide communication lines and data transmission. Such cable lines include fiber optic lines which are used for high speed communication by transmitting light pulses as high bit rate digital signals. Conduits containing such fiber optic lines often run along railroad beds and are exposed to ambient air temperatures on railroad bridges which cross over highways, rivers, etc. Another place fiber optic cables are installed is in old unused gas pipelines. When installed in such old pipelines, fiber optic conduits are also exposed to ambient temperatures at stream crossings and other exposed areas.
It has been found that fiber optic lines show increased attenuation (signal degradation) during cold weather, limiting their ability to send high bit rate digital signals. During cold weather, ice forms in the water contaminated cable conduit lines which are exposed to subfreezing temperatures such as on railroad bridges over highways. The ice exerts pressure on the cable, causing microbending and increased attenuation of the fiber optic signal. It has been found that this phenomenon is reversible in that the fiber optic cable lines usually return to their normal attenuation when temperatures return to above freezing.
Several approaches have been tried to prevent water ingress and ice formation in cable conduits. Two-part liquid rubbers have been pumped into the conduits where they cure to form a water barrier. However, this procedure is very expensive and variations in cure and thickening rates make fill distances hard to control. Also, curable water impervious materials can actually trap existing ice against the cable by flowing and curing around it. Various water repellent greases have also been used which are heated, liquified, and pumped into the cable conduit. However, such materials are generally not compatible with cable jackets over the long term, are environmentally undesirable on leakage into the soil, and are difficult to control in their gelling times and behavior with existing ice and water in the conduit.
Therefore, the need exists for a composition which stays in a cable conduit and surrounds a cable therein, which does not adversely affect cable jackets or the environment, and which prevents ice formation from both water ingress and existing ice and water in the conduit.